Pulsed Carbon Dioxide Laser for Cartilage Vaporization and Subchondral Bone Perforation in Horses Part II: Morphologic and Histochemical Reactions

A pulsed carbon dioxide laser was used to vaporize articular cartilage in four horses, and perforate the cartilage and subchondral bone in four horses. Both intercarpal joints were examined arthroscopically and either a 1 cm cartilage crater or a series of holes was created in the third carpal bone of one joint. The contralateral carpus served as a control. After euthanasia at week 8, the treated and control joints were examined for gross changes, and samples of cartilage and subchondral bone, synovial membrane, and peripheral lymph nodes were examined histologically. Depletion of cartilage matrix glycosaminoglycan was assessed by safranin-O histochemical staining of the laser site and adjacent cartilage. Cartilage removal by laser vaporization resulted in rapid regrowth, with fibrous and fibrovascular tissue and occasional regions of fibrocartilage at week 8. The subchondral bone, synovial membrane, and draining lymph nodes appeared essentially unaffected by the laser cartilage vaporization procedure. Conversely, carbon dioxide laser drilling of subchondral bone resulted in poor penetration, extensive areas of thermal necrosis of bone, and significant secondary damage to the apposing articular surface of the radial carpal bone.     

The Intercarpal Ligaments of the Equine Midcarpal Joint, Part 3: Clinical Observations in 32 Racing Horses With Midcarpal Joint Disease

Objective— To characterize the clinical features of intercarpal ligament pathology and to determine the relationship among palmar intercarpal ligament tearing, dorsomedial intercarpal ligament (DMICL) hypertrophy, and other intraarticular lesions.
Study Design— Prospective clinical observations.
Animals or Sample Population— Twenty-eight thoroughbred and four standardbred race horses.
Methods— Clinical, radiographic, and arthroscopic examination of 53 midcarpal joints of 32 horses.
Results— Palmar intercarpal ligament tearing was observed in 30 joints of 22 horses. Some tearing of the medial palmar intercarpal ligament (MPICL) was present in 27 joints of 20 horses, and tearing of the lateral palmar intercarpal ligament in 9 joints of 7 horses. There was no correlation between the severity of clinical signs recorded and the degree of MPICL tearing. Joints with grade 2–4 MPICL tearing had significantly less cartilage and bone damage than joints with grade 1 or no ligament damage ( P <.05). There was a significant inverse relationship between the number and size of intra-articular fractures, as assessed radiographically, and ligament damage ( R = -.31). The DMICL was identified in all joints, and in 18 joints the ligament was enlarged. There was a significant correlation between MPICL damage and hypertrophy of the DMICL ( R =.35). There was no correlation between DMICL hypertrophy and articular cartilage damage or subchondral bone damage.
Conclusions— Severe subchondral bone and MPICL damage rarely occur in the same joint and DMICL hypertrophy may be associated with, rather than a cause of, joint disease.
Clinical Relevance— There are no clinical or radiographic findings that will differentiate intercarpal ligament injury from other carpal injuries. Diagnosis is only possible by arthroscopic examination of the midcarpal joint.     

The effect of intra-articular methylprednisolone acetate and exercise on equine carpal subchondral and cancellous bone microhardness

Dorsal carpal osteochondral injury is a major cause of lameness in horses undergoing high intensity training. Intra-articular corticosteroid treatment is used commonly to manage exercise-associated articular pain, but its use remains highly controversial in the equine athlete. This project, therefore, aimed to compare the mechanical properties of intra-articular MPA and diluent-treated middle carpal subchondral and cancellous bone in horses undergoing a short-term treadmill exercise programme. It was hypothesised that subchondral and cancellous bone mechanical properties are influenced by intra-articular administration of methylprednisolone acetate (MPA). Eight 2-year-old female horses had MPA or diluent administered into contralateral middle carpal joints at 14 day intervals, for a total of 4 treatments per horse. Horses underwent a standard treadmill exercise protocol until euthanasia (Day 70). Standard sites were located on the dorsal aspect of third, radial and intermediate carpal bones. Osteochondral samples from each test site were divided into subchondral bone and cancellous bone portions. These were dried, resin-embedded and gold-coated. Microhardness measurements were obtained at each test site. No significant effect of intra-articular treatment was detected. At each site, cancellous bone trabecular struts had an 18-19% higher microhardness value than the overlying subchondral bone. These findings indicate that intra-articular administration of MPA at this dose has no effect on subchondral or cancellous bone adaptation to short-term exercise and, therefore, on the propensity of carpal bones to injury. Further investigation into the calcified cartilage layer, effect of different corticosteroid preparations and diffusion of medication are required.     

Accuracy of Arthroscopic Identification of Equine Carpal Lesions

The equine carpal joint was used to evaluate arthroscopic diagnosis of lesions created in joints obtained from horses euthanized for reasons other than lameness. Full-thickness articular defects were made in 13 sites within the antebrachiocarpal joint and middle carpal joint approximating those found in diseased carpal joints. Arthroscopic evaluation of the lesions included location, depth, and size of the defects. The joints were subsequently examined grossly. Results showed that, when compared to gross evaluation, arthroscopy is capable of accurately identifying subtle changes in articular cartilage and bone. A statistically significant increase in error rate was found for lesions at the medial aspect of the proximal radial carpal bone. Other sites with limited arthroscopic access were the proximal ulnar carpal bone, the proximal fourth carpal bone, and the distal intermediate carpal bone. The accuracy of arthroscopic identification of lesions improved significantly during the study as experience with the technique was gained.     

Fate and effect of autogenous osteochondral fragments implanted in the middle carpal joint of horses.

Four autogenous osteochondral fragments removed from the lateral trochlear ridge of the talus were arthroscopically placed as loose bodies in a randomly selected middle carpal joint in each of 10 horses. The contralateral middle carpal joint, subjected to a sham procedure, served as control. Postoperative treatment was consistent with that for clinical arthroscopic patients. Lameness evaluation, radiographic examination, carpal circumference measurement, and synovial fluid analysis were performed before and at scheduled intervals after surgery. After a 2-month confinement, horses were subjected to an increasing level of exercise. Horses were euthanatized at intervals through 6 months. Gross and microscopic evaluations were performed on remaining fragments, articular cartilage, and synovial membrane of each middle carpal joint. Increased joint circumference, effusion, lameness, and degenerative joint disease distinguished implanted from control joints over the 6-month period. Implanted joints were characterized by grooved, excoriated cartilage surfaces, and synovium that was thick, erythematous, and irregular. At 4 weeks, implants were found to have adhered to synovium at their subchondral bone surface. The bone within fragments was undergoing necrosis, while cartilage was preserved. At 8 weeks, fragments were radiographically inapparent, grossly evident as pale plaques on the synovial surface, and composed of dense fibrous connective tissue. Synovial membrane specimens from implanted joints had inflammatory change characterized by mononuclear cell infiltration 2 months after implantation. Physical damage was apparent within articular cartilage of implanted joints at 2 months, and was significant (P less than 0.05) at 6 months after surgery. Chondrocyte degenerative change was significant (P less than 0.05) at 6 months after surgery. Focal reduction in safranin-O uptake was observed in cartilage layers adjacent to physical defects. Osteochondral loose bodies of the size implanted in the middle carpal joint of horses in this study were resorbed by the synovium within 2 months. Synovitis and significant articular cartilage damage were associated with the implanted fragments. Regardless of origin, free osteochondral fragments within the middle carpal joint should be removed, and methods to prevent residual postoperative debris should be implemented to reduce potential for articular pathologic change.     

Luxation and/or fracture of the first carpal bone in thoroughbred horses and its surgical resolution

A syndrome involving luxation and/or fracture of the first carpal bone is described. Affected horses have a grade 1-3 lameness, which responds to intra-articular anesthesia of the intercarpal joint. Medical treatment has not be successful in relieving lameness, and the treatment of choice is surgical removal of the first carpal bone.     

Effects of polysulfated glycosaminoglycan on chemical and physical defects in equine articular cartilage

The effect of intra-articular polysulfated glycosaminoglycan (PSG) on repair of chemical and physical articular cartilage injuries was evaluated in 8 horses. In each horse, a partial- and a full-thickness articular cartilage defect was made on the distal articular surface of the radial carpal bone. In the contralateral middle carpal joint, a chemical articular cartilage injury was induced by injecting 50 mg of Na monoiodoacetate (MIA). Four of the 8 horses were not treated (controls), and 4 horses were treated by intra-articular injection of 250 mg of PSG into both middle carpal joints once a week for 5 treatments starting 1 week after cartilage injury. Horses were maintained for 8 weeks. There was less joint circumference enlargement in PSG-treated horses in MIA-injected and physical defect carpi, compared with that in controls. In MIA-injected joints, there was less articular cartilage fibrillation and erosion, less chondrocyte death, and greater safranin-O staining for glycosaminoglycans in PSG-treated horses. Evaluation of joints in which physical defects were made revealed no differences between control and PSG-injected joints. None of the partial-thickness defects had healed. Full-thickness defects were repaired with fibrous tissue (which was more vascular and cellular in PSG-injected joints) and occasionally small amounts of fibrocartilage. Seemingly, PSG had chondroprotective properties in a model of chemically induced articular cartilage damage, whereas PSG had no obvious effect in a physical articular cartilage-defect model.     

Effects of intra-articular administration of methylprednisolone acetate on normal articular cartilage and on healing of experimentally induced osteochondral defects in horses.

The effects of intra-articular administration of methylprednisolone acetate (MPA) on the healing of full-thickness osteochondral defects and on normal cartilage were evaluated in 8 horses. In group-1 horses (n = 4), a 1-cm-diameter, full-thickness defect was created bilaterally in the articular cartilage on the dorsal distal surface of the radial carpal bone. Cartilage defects were not created in group-2 horses (n = 4). One middle carpal joint was randomly selected in each horse (groups 1 and 2), and treated with an intra-articular injection of 100 mg of MPA, once a week for 4 treatments. Injections began 1 week after surgery in group-1 horses. The contralateral middle carpal joint received intra-articular injections of an equivalent volume of 0.9% sodium chloride solution (SCS), and served as a control. Horses were evaluated for 16 weeks, then were euthanatized, and the middle carpal joints were examined and photographed. Synovial and articular cartilage specimens were obtained for histologic and histochemical evaluation. Gross morphometric evaluation of the healing defects in group-1 horses revealed that 48.6% of the defect in control joints and 0% of the defect in MPA-treated joints was resurfaced with a smooth, white tissue, histologically confirmed as fibrocartilage. This replacement tissue was a firmly attached fibrocartilage in control joints and a thin fibrous tissue in MPA-treated joints. The articular cartilage in joints treated with MPA had morphologic changes, including chondrocyte cluster formation, loss of palisading architecture, and cellular necrosis in both groups of horses.(ABSTRACT TRUNCATED AT 250 WORDS)     

The incidence and severity of intercarpal ligament damage in the equine carpus

SUMMARY The arthroscopic findings in 104 intercarpal joints in 76 horses were reviewed to determine the incidence and severity of changes in the medial intercarpal ligament. Damage to the intercarpal ligament was observed in 43 joints in 35 horses, ranging from mild fraying of the edges of the ligament to complete disruption of all fibres. This represented an incidence of 41% of joints being affected. In 9 joints examined arthroscopically primarily as a further diagnostic procedure, ligament damage was evident in all cases. In horses undergoing arthroscopic surgery primarily for the treatment of osteochondral chip or slab fractures, there was some correlation between the severity of articular cartilage damage and the presence of ligament damage.     

Healing of full-thickness cartilage compared with full-thickness cartilage and subchondral bone defects in the equine third carpal bone.

The effect of lesion depth on the quality of third carpal bone cartilage repair was examined. A 1-cm diameter articular defect penetrating the calcified cartilage in one limb and the subchondral bone plate in the opposite limb was created in the radial facet of the third carpal bones. Clinical and xeroradiographic examinations were performed every 4 weeks until 4 months (3 horses) and 6 months (3 horses) after surgery. The synovial membrane, non-opposing articular surfaces and articular defects were examined grossly, histologically and histochemically. Grossly, deeper defects contained thicker, whiter tissue, but both joints contained generalised degenerative changes. Defects extending through calcified cartilage were filled deeply by fibrocartilage and superficially by fibrous connective tissue. Defects extending through subchondral bone were consistently filled with hyaline-like cartilage in the depths of the lesion, fibrocartilage in the intermediate layer and fibrous connective tissue superficially. The results indicate that subchondral bone is the source of hyaline-like cartilage repair tissue and suggest that quality of healing of cartilage defects may be improved by penetrating the subchondral bone plate. It also appears that the synovitis associated with the procedure must be controlled before the procedure can be advocated for treatment of clinical cases.     

Clinical effects of betamethasone and hyaluronan,and of defocalized carbon dioxide laser treatment on traumatic arthritis in the fetlock joints of horses

The clinical effects of intra-articular betamethasone together with hyaluronan (betaM/HA) and treatment with a defocalized carbon dioxide laser on acute traumatic arthritis of the fetlock joint were assessed. The horses in these studies were selected using a thorough lameness examination, including intra-articular anaesthesia abolishing the lameness. This investigation comprised an observer-blind study, including 10 sport horses (10 joints), and a prospective study, including 180 sport horses (333 joints). In both studies, the material was divided into two groups treated with either betaM/HA or a carbon dioxide laser. The treatment doses were 12 mg of betaM, 20 mg of HA or 60 J/cm2 of treated area. Convalescence before training was 21 days for both groups in the observer-blind study. In the prospective study, convalescence in the betaM/HA group was 21 days but was only 7 days for the laser-treated group. In the observer-blind study, three of five treated joints recovered in both cohorts. In the prospective study, the groups had significantly different recovery rates--68% of the betaM/HA-treated joints and 80% of the carbon dioxide laser-treated joints. These results indicate that the defocalized carbon dioxide laser should be an applicable mode of treatment of acute traumatic synovitis in horses. However, the biochemical functions related to carbon dioxide laser treatment require further elucidation.     

Arthroscopic findings in horses with subtle radiographic evidence of osteochondral lesions of the medial femoral condyle: 15 cases (1995-2002)

OBJECTIVE: To determine arthroscopic findings in lame horses with subtle radiographic lesions of the medial femoral condyle. DESIGN: Retrospective study. ANIMALS: 15 horses examined because of lameness that had subtle radiographic evidence of osteochondral lesions involving the medial femoral condyle in at least 1 joint. PROCEDURE: Medical records were reviewed, and results of physical examination, radiography, and arthroscopy were recorded. Follow-up information was obtained through reexamination of the horses or telephone conversations with the referring veterinarians, owners, or trainers. RESULTS: Lameness severity ranged from grade 1 to 3 on a scale from 0 to 5. Radiography and arthroscopy were performed on 28 stifle joints. The 4 unaffected joints in 4 horses with unilateral hind limb lameness that underwent bilateral arthroscopy had no radiographic lesions, but 2 of the 4 had arthroscopic lesions. Of the remaining 24 joints, 20 had radiographic evidence of flattening of the apex of the medial femoral condyle and 4 had minimal subchondral lucency. Lesions were identified arthroscopically in 18 of the 20 joints with flattening of the condyle and in all 4 joints with subchondral lucency. Treatment consisted of abrasion arthroplasty or microfracture. Seven of the 9 horses with focal cartilage lesions and 2 of the 6 horses with generalized cartilage lesions were reportedly sound without any evidence of joint effusion at the time of final follow-up. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that horses with hind limb lameness and subtle radiographic lesions of the medial femoral condyle are likely to have arthroscopically apparent cartilage lesions and subchondral bone defects.     

In vivo kinetic study on uptake and distribution of intramuscular tritium-labeled polysulfated glycosaminoglycan in equine body fluid compartments and articular cartilage in an osteochondrial defect model

The uptake and distribution of intramuscularly (IM) administered tritium-labeled polysulfated glycosaminoglycan (³H-PSGAG) in serum, synovial fluid, and articular cartilage of eight horses was quantitated, and hyaluronic acid (HA) concentration of the middle carpal joint was evaluated in a pharmacokinetic study. A full-thickness articular cartilage defect, created on the distal articular surface of the left radial carpal bone of each horse served as an osteochondral defect model. ³H-PSGAG (500 mg) was injected IM, between 14 and 35 days after creation of the defects. Scintillation analysis of serum and synovial fluid, collected from both middle carpal joints at specific predetermined times up to 96 hours post-injection, revealed mean ³H-PSGAG concentrations peaked at 2 hours post-injection. ³H-PSGAG was detected in cartilage and subchondral bone 96 hours post-injection in samples from all eight horses. There were no statistically significant differences in ³H-PSGAG concentration of synovial fluid or cartilage between cartilage defect and control (right middle carpal) joints.

HA assay of synovial fluid revealed concentrations significantly increased at 24, 48, and 96 hours post-injection in both joints. The concentration nearly doubled 48 hours post-injection. However, no statistically significant differences were found between synovial concentrations of HA in cartilage defect and control joints.

³H-PSGAG administered IM to horses, was distributed in the blood, synovial fluid, and articular cartilage. HA concentrations in synovial fluid increased after IM administration of polysulfated glycosaminoglycan.     

Validation of magnetic resonance imaging for measurement of equine articular cartilage and subchondral bone thickness

OBJECTIVE: To validate use of magnetic resonance images (MRIs) for measurement of equine articular cartilage and subchondral bone thickness by comparison with measurements in histologic specimens. SAMPLE POPULATION: 32 cadaveric carpal joints from 16 horses. PROCEDURE: Magnetic resonance imaging was performed by use of 3-dimensional fast spoiled gradient echo (SPGR) and T2* 3-dimensional fast gradient echo (GRE) pulse sequences with and without fat saturation. Standard sites on the medial and lateral facets of the intermediate, radial, and third carpal bones were used for subchondral bone and articular cartilage thickness measurements. Digital image analysis software was used for MRI measurements 10 mm from the dorsal extent and perpendicular to the articular surface. Histomorphometric measurements of hyaline, calcified cartilage, and subchondral bone thickness were obtained at selected sites. Comparisons between histomorphometric and MRI measurements and between magnetic resonance pulse sequences were evaluated. RESULTS: There were significant correlations between GRE and SPGR and SPGR and histologic measurements of articular cartilage, with no significant difference between measurements and good agreement. When calcified cartilage was excluded from the histologic measurement, MRI measurements were significantly greater than histologic measurements. For subchondral bone thickness, there was significant correlation between GRE and SPGR but GRE was significantly greater than SPGR measurements. Histomorphometric and MRI measurements were strongly correlated and not significantly different. CONCLUSIONS AND CLINICAL RELEVANCE: Magnetic resonance imaging provides a good representation of cartilage and subchondral bone thickness, supporting its use in the study and clinical diagnosis of osteochondral structure and alteration.     

Morphological Effects of Arthroscopic Partial Synovectomy in Horses

Gross and microscopic effects of arthroscopic partial synovectomy on synovium and articular cartilage of middle carpal joints were studied in 15 horses. A 7-mm diameter motorized synovial resector was inserted into each middle carpal joint and arthroscopic partial synovectomy and lavage or arthroscopic lavage alone was performed. Study periods were 0 (three horses), 16 (three horses), and 30 days (six horses). No gross evidence of degenerative joint disease was observed at day 16 or 30. At 30 days, resected areas lacked villi and there was deposition of fibrin on the synovial surface with varying amounts of newly formed fibrovascular tissue. Thirty days after arthroscopic synovectomy, normal synovium had not formed in equine middle carpal joints.     

Arthroscopic approaches to the palmar aspect of the equine carpus

OBJECTIVE: To identify sites for arthroscopic access to the palmar aspects of the antebrachiocarpal (AC) and middle carpal (MC) joints, and describe visible carpal bone surfaces for each approach. STUDY DESIGN: Prospective experimental study. ANIMALS: Equine carpi: 16 cadavers, 8 live horses. METHODS: A latex model was used to identify possible sites for arthroscopic access to the palmar aspects of the AC and MC joints. Carpi (n = 24) were examined arthroscopically and arthroscopic access sites and visible carpal bone surfaces were described. RESULTS: Arthroscopic approaches and instrument portals were developed for the medial and lateral aspects of the palmar pouches of the AC and MC joints. The palmar surface of the radial carpal bone and radius, and the dorsal articular surfaces of the accessory carpal bone, could be viewed using palmar approaches to the AC joint. The palmar aspect of the radial, third and second carpal bones (medially) and ulnar and fourth carpal bones (laterally) could be observed using a palmar approach to the MC joint. CONCLUSIONS: Arthroscopic access, using separate medial and lateral portals to the AC and MC joints, allowed assessment of portions of the caudodistal radius, the palmar surfaces of the radial, ulnar, second, third and fourth carpal bones, and the dorsal aspect of the accessory carpal bone. CLINICAL RELEVANCE: Arthroscopic approaches to the palmar aspect of the carpus could be used to remove fracture fragments, and to assess the medial palmar intercarpal ligaments.     

Evaluation of intra-articularly administered sodium monoiodoacetate-induced chemical injury to articular cartilage of horses.

Three doses of sodium monoiodoacetate (MIA) were used to induce degenerative changes in articular cartilage in middle carpal joints of horses. Twelve young (2- to 5-year-old) horses, free of lameness, were randomly allotted to 3 groups. One middle carpal joint of each horse was injected with 0.9% NaCl solution (control joint). The contralateral middle carpal joint was injected with 0.09 mg of MIA/kg of body weight (group 1); 0.12 mg/kg (group 2); or 0.16 mg/kg (group 3). After MIA administration, horses were allowed ad libitum exercise in a 2-acre paddock for 12 weeks. At the end of the study, gross and microscopic tissue changes were evaluated and biochemical analyses of articular cartilage were done. Grossly, diffuse partial-thickness articular cartilage lesions were observed in group-2 (n = 2) and group-3 (n = 4) horses, but not in group-1 horses. Articular cartilage uronic acid content was significantly (P less than 0.03) decreased in all MIA-injected joints, compared with controls. Articular cartilage matrix staining with safranin-O was decreased in 3 of 4 MIA-injected joints of group-1 horses and in all MIA-injected joints of group-2 and group-3 horses, compared with controls (P less than 0.06). Microscopic degenerative changes in articular cartilage were not significantly different between MIA-injected and control joints in group-1 horses, but were increased (P less than 0.06) in all MIA-injected joints of group-2 and group-3 horses, compared with controls. Qualitatively, decreased matrix staining and degenerative changes were more severe in group-3 horses. On the basis of articular cartilage gross and microscopic changes, as well as biochemical changes, 0.12 mg of MIA/kg injected intra-articularly was determined to induce moderate degrees of articular cartilage degeneration. This model of chemically induced articular cartilage injury could be useful for evaluating treatment effects of anti-arthritic drugs in horses.     

Arthroscopic Surgery for the Treatment of Osteochondritis Dissecans in the Equine Femoropatellar Joint

Forty limbs with femoropatellar osteochondritis dissecans in 24 horses were treated with arthroscopic surgery. Lesions were bilateral in 16 horses and unilateral in eight horses. Diagnostic examination and surgical treatment were performed through a single arthroscopic portal; five different instrument portal locations and six instrument approaches were used. Lesions were localized to the lateral trochlear ridge of the femur in 31 affected joints, medial trochlear ridge in two joints, lateral and medial trochlear ridges together in two joints, lateral trochlear ridge plus patella in four joints, and patella alone in one joint. The lesions consisted of subchondral defects containing chondral or osteochondral flaps or fragments, or were seen as dimpling, cracking, fibrillation, or erosion of articular cartilage, or intact cartilage over a subchondral defect. Loose bodies were found in three joints. There was a poor correlation between radiologic and arthroscopic findings. Surgical manipulations included removal of flaps, fragments, and undermined articular cartilage, and debridement of the subchondral defect. Three horses were euthanized: one electively to assess the joint grossly, one because of complications following surgery and salmonellosis, and one because of unrelated forelimb abnormalities. Immediate clinical improvement after surgery was seen in the 22 horses permitted to survive. Long-term follow-up on seven of 10 racehorses revealed that two have raced successfully, two are "ready to race," three are training sound, two are sound at pasture (still in convalescence), and one has been reoperated. Of six horses used for show or pleasure, three are being shown sound, one is sound for pleasure, and two are training sound. The remaining horses are convalescing.     

Diagnostic findings and prognosis following arthroscopic treatment of subtle osteochondral lesions in the shoulder joint of horses: 15 cases (1996-1999)

OBJECTIVE: To determine clinical, scintigraphic, radiographic, and arthroscopic findings and results of treatment in horses with lameness attributable to subtle osteochondral lesions of the shoulder joint. DESIGN: Retrospective study. ANIMALS: 15 horses. PROCEDURE: Medical records were reviewed, and results of physical examination, scintigraphy, radiography, arthroscopy, and treatment were recorded. RESULTS: Severity of lameness ranged from grade 1 to 4. Response to shoulder flexion or extension was variable. Twelve horses had a narrow upright foot. Intra-articular anesthesia of the shoulder joint localized the cause of the lameness to the shoulder joint in 9 of 10 horses. Scintigraphic abnormalities were detected in 4 of 6 horses. Radiographic lesions were subtle and included glenoid sclerosis, focal glenoid lysis, small glenoid cysts, and alterations in the humeral head contour. Arthroscopic evaluation confirmed clefts in the glenoid cartilage, glenoid cysts, a humeral head cyst, fibrillation of the humeral head cartilage, cartilage fragmentation, or a nondisplaced fracture of the humeral head. After treatment, 12 horses returned to their previous level of performance, 1 was sound for light riding, 1 remained lame, and 1 was euthanatized because of chronic lameness. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that a combination of physical examination, scintigraphy, and radiography is necessary to diagnose subtle osteochondral lesions of the shoulder joint in horses. Arthroscopy can be used to confirm the diagnosis and treat cartilage and subchondral bone lesions. Young and middle-aged horses with subtle osteochondral lesions of the shoulder joints have a good prognosis for return to performance following arthroscopic treatment.     

Effects of intramuscular polysulfated glycosaminoglycan on chemical and physical defects in equine articular cartilage.

The effect of intramuscular polysulfated glycosaminoglycan (PSG) on repair of cartilage injury was evaluated in eight horses. In each horse, one middle carpal joint had both a partial-thickness and a full-thickness articular cartilage defect created. In the contralateral middle carpal joint, chemical articular cartilage injury was created by intra-articular injection of 50 mg sodium monoiodoacetate (MIA). Horses were divided into two groups for treatment. Group 1 horses (control) received an intramuscular injection of normal saline every four days for a total of seven injections starting seven days after cartilage injury. Group 2 horses received 500 mg of PSG intramuscularly every four days for seven treatments starting seven days after cartilage injury. Horses were maintained for 12 weeks. Horses were evaluated clinically, and their middle carpal joints were evaluated radiographically and arthroscopically at the end of the study. Joint tissues were also collected and examined microscopically. The only significant difference between groups was slightly greater matrix staining intensity for glycosaminoglycans in the radiate articular cartilage layer in MIA injected and PSG treated joints. Partial-thickness defects had not healed and the predominant repair tissue in full-thickness defects was fibrous tissue. It was concluded that using this joint injury model, 500 mg PSG administered intramuscularly had no effect on the healing of articular cartilage lesions, and minimal chondroprotective effect from chemically induced articular cartilage degeneration.